In general, an electric generator is largely classified into an alternating current generator and a direct current generator. The alternating current generator includes a rotor, a stator formed at the outside of the rotor, and a hollow cylindrical casing that holds the stator. When the rotor is rotated, a magnetic flux generated from a magnet of the rotor interacts with a winding wire of the stator to induce electric current in the winding wire of the stator. Generally, the stator is concentrically disposed within a casing of the rotor, and includes a soft magnetic core and an electrically conductive winding wire. Electric power supplied by the alternating current generator varies depending on the rotational speed of the rotor. In this case, the stator may be concentrically disposed within the rotor in an alternating manner. In other words, an alternating current power generation principle is as follows. An N-pole is arranged at a left side and an S-pole is arranged at a right side, and a coil continues to be rotated in a counterclockwise direction in a state of being perpendicular to a magnetic line of force. When the coil is rotated by 0 to 90 degrees, the magnetic flux generated from the coil is increased, and an N-pole side coil and an S-pole side coil simultaneously produce an induced electromotive force in a counterclockwise direction. In addition, when the coil is rotated by 90 to 180 degrees, the magnetic flux generated from the coil is decreased, and the N-pole side coil and the S-pole side coil simultaneously produce an induced electromotive force in a clockwise direction so as to generate electric current.
In the meanwhile, the direct current generator includes a rot or, a stator formed at the outside of the rotor, and a hollow cylindrical casing that holds the stator. When the rotor is rotated, a magnetic flux generated from a magnet of the rotor interacts with a winding wire of the stator to induce electric current in the winding wire of the stator. Generally, the stator is concentrically disposed within a casing of the rotor, and includes a soft magnetic core and an electrically conductive winding wire. Electric power supplied by the direct current generator varies depending on the rotational speed of the rotor. In this case, the stator may be concentrically disposed within the rotor in an alternating manner.